1. Field of the Invention
The invention relates to an electronic wireless tire pressure monitoring apparatus, and more particularly, to a monitoring apparatus whose electronic detecting unit and power supply are set outside the tire. Accordingly, the signal transmission, battery renewal and the maintenance can be carried out directly outside the tire.
2. Description of the Related Art
After some time of driving, exposure to the sunlight or the fall of temperature at night, the tire may leak to some extent and the tire pressure will fall down under a normal pressure of 28 psi. It brings a potential danger for the driving safety. Particularly, if one tire of a high speeding vehicle due to the insufficient tire pressure breaks up, the result is very destructive.
Therefore, plenty of researchers have been devoting to developing this kind of detecting and monitoring devices that monitor the tire pressure during driving. Such disclosures include TW 536489, TW 400811, TW 149143, TW 177543, TW 560445, TW 574977, TW 090946, TW 100539, TW 396974, etc. The working principles of above mentioned patents can be divided into electronic detecting and mechanical detecting groups. The life span of the mechanical one is relatively shorter, and the device body is bigger and the detecting precision is not good at the same time. Such kind of mechanical detecting devices is not the object of the invention so that no further descriptions thereto are given hereinafter.
The most popular design of electronic tire pressure detecting apparatus is the hidden mounting construction in the steel wheel rim for the tire. Such kind of apparatus has been disclosed in TW 404354, TW 578706, TW 578707, etc. The advantage of the design is that the tire pressure can be measured directly by the hidden tire pressure monitoring apparatus inside of the tire. The main structure is shown in FIGS. 1 and 2. It consists of a body (11) and a detecting circuit board (12) which is set in the body (11). This circuit board (12) has a signal transmission antenna (13) and two batteries (14) which supply power to this circuit board (12). In the front of the body, an air inlet (15) is mounted. When the above described components are assembled into a tire pressure monitoring apparatus (10) (shown in the FIG. 2), the whole set will be fixed on a steel wheel rim (21) inside of the tire (20). The air inlet (15) penetrates this steel wheel rim (21) and it is fastened by a plate (16) and a screw (17). At last a protecting head (18) will be screwed up and the assembly is finished.
The above mentioned conventional tire pressure monitoring apparatus (10) will transmit a signal through the signal transmission antenna (13), when it detects an abnormal tire pressure. The warning signal will be received by a receiver (not shown in the drawings) in the vehicle and the driver acquires a message about the abnormal tire pressure. However, the signal transmission antenna (13) is mounted in the tire (20), it may be shielded and the signal transmission will be interfered. This leads to an unsatisfying precision and reliability. This is the defect of this mentioned tire pressure monitoring apparatus.
U.S. Pat. No. 5,798,689 discloses another type of tire pressure monitoring apparatus which is mounted inside of the tire. Just like the mentioned one in the above patents, it shows also a hidden design. Another further disadvantage is that the power of this hidden type tire pressure monitoring apparatus is supplied by battery. The battery must be changed frequently due to the limited electricity capacity, but the whole set of tire pressure monitoring apparatus is hidden in the tire and it brings great difficulty and inconvenience to the job of battery changing. By changing the battery, the wheel must be removed firstly from the vehicle, air pressure within the tire has to be released, then the tire must be taken out and the tire pressure monitoring apparatus has to be disassembled. Now the battery can be changed. Thereafter, assembly should be carried out according to the opposite sequence. So, it is very difficult and inconvenient to change the battery.